This invention relates to a method and apparatus for preventing copying of video signals which are intended to be copy protected and more particularly is directed to prevention of unauthorized copying of video signals transmitted or received by a digital video tape recorder (VTR).
There has been proposed a VTR for consumer use in which program information in the form of a video signal and an associated audio signal are recorded in digital form on a magnetic tape. Digital recording of video signals and associated audio signals make it possible for such program information to be reproduced and copied (or "dubbed") onto another tape with little or no deterioration in the quality of the signal reproduced from the copy tape. These are times, however, when it is desirable to prevent such signals from being recorded. For example, in order to protect the rights of those holding a copyright in the recorded material, copyright protection schemes have been proposed in which the digital recording format includes a bit for indicating that copying of the recorded digital video signal is to be inhibited. Such proposed copy protection systems are designed to prevent unauthorized copying of a signal that is transmitted in digital form from one digital VTR to another.
With respect to digital VTRs that can provide analog video and audio output and can receive analog video and audio signals as input signals, transmission of the video and audio signals in analog form from one digital VTR to another permits the receiving VTR to record a very high quality signal in digital form. The previously proposed copy protection systems for digital VTRs are not effective to prevent a digital VTR from recording a signal received in analog form, and the high quality of the resulting copies makes such copies a significant threat to the interests of those owning rights in the program information, such as copyright holders.
Moreover, there are a number of other sources of protectable program information in the form of video signals besides analog or digital video outputs from digital VTRs. Among these are television program signals broadcast from conventional terrestrial stations, television programs broadcast from satellites, video signals output from video disk players, television programming distributed by cable, and pay-per-view programming distributed by satellite or by cable. In some cases the broadcast signal may be free of any copyright but in other cases copyright is asserted. It is desirable that copying of the signals be prevented when a copyright is asserted with respect to the material represented by the signal or when the owner of such program information wishes to prevent unauthorized copying thereof.